This invention relates to a high tension-strong current transformer immersed in a dielectric fluid such as an electrically insulating oil.
A conventional current transformer of the type referred to has previously comprised a primary winding in the form of a tubular electrically conducting coil which forms a single turn enclosed with an electrically insulating member and a secondary winding in the form of a tubular electrically conducting coil electromagnetically coupled to the primary winding through the electrically insulating member. The primary winding includes a pair of lead-in wires consisting of a pair of coaxial tubular electrically conducting members connected to both ends thereof respectively to form an incoming and an outgoing flow path for a dielectric fluid such as an electrically insulating oil communicating with the interior of the primary coil. An outer one of the coaxial tubular members has been enclosed with an extension of the electrically insulating member for the primary coil.
Then the primary and secondary windings have been immersed in the dielectric fluid within an enclosing housing while the flow paths and the interior of the primary coil are filled with the dielectric fluid.
In operation the primary winding has generated heat and particularly an inner one of the coaxial tubular member has been thermally affected by the outer tubular member to be higher in temperature than the outer tubular member, resulting in the occurrence of a difference in temperature of the electrically insulating oil between the outgoing flow path within the inner tubular member and the incoming flow path between the outer and inner tubular members. Thus that portion of the oil located in the outgoing flow path has ascended therealong until it is delivered to the upper portion of the housing through the upper end of the inner tubular member. On the upper portion of the housing, the electrically insulating oil at an elevated temperature has dissipated its heat to the air through a peripheral wall thereof to be cooled. The cooled oil has then descended along the incoming flow path to reach the primary coil, thereby to cool the latter.
Under these circumstances, the funnel effect is caused from both an ascending stream of the electrically insulating oil flowing along the outgoing flow path and the total length of incoming and outgoing flow paths to perform the thermal syphon operation with the result that the primary winding continues to be cooled.
However the thermal syphon operation exhibits the effect affected by the heat exchange between the primary winding and the electrically insulating oil to be proportional to an area over which the heat exchange is effected. This means that, with the incoming and outgoing flow paths formed of the pair of coaxial tubular members, the area of heat exchange between the inner tubular member and the electrically insulating oil has, as a matter of course, a limitation as to the dimension. Thus, if it is attempted to apply a primary winding with the pair of coaxial tubular members as described above to a current transformer operated with higher currents, it has been required to render the area of heat exchange of the inner tubular member sufficiently large, which is attended with the outer tubular member large in outside diameter. Consequently, the current transformer itself has been large, resulting in the disadvantage that it is economically unfavorable.
Accordingly, it is an object of the present invention to provide a new and improved current transformer having an excellent cooling effect by increasing the area of heat exchange as much as possible without increasing the size of the primary winding as a whole.